Real-time simulation of multibody systems with applications for working mobile vehicles

摘要

This dissertation describes an approach for developing a real-time simulation for workingmobile vehicles based on multibody modeling. The use of multibody modeling allowscomprehensive description of the constrained motion of the mechanical systems involvedand permits real-time solving of the equations of motion. By carefully selecting themultibody formulation method to be used, it is possible to increase the accuracy of themultibody model while at the same time solving equations of motion in real-time.In this study, a multibody procedure based on semi-recursive and augmented Lagrangianmethods for real-time dynamic simulation application is studied in detail. In the semirecursiveapproach, a velocity transformation matrix is introduced to describe thedependent coordinates into relative (joint) coordinates, which reduces the size of thegeneralized coordinates. The augmented Lagrangian method is based on usage of globalcoordinates and, in that method, constraints are accounted using an iterative process.A multibody system can be modelled as either rigid or flexible bodies. When usingflexible bodies, the system can be described using a floating frame of referenceformulation. In this method, the deformation mode needed can be obtained from the finiteelement model. As the finite element model typically involves large number of degreesof freedom, reduced number of deformation modes can be obtained by employing modelorder reduction method such as Guyan reduction, Craig-Bampton method and Krylovsubspace as shown in this studyThe constrained motion of the working mobile vehicles is actuated by the force from thehydraulic actuator. In this study, the hydraulic system is modeled using lumped fluidtheory, in which the hydraulic circuit is divided into volumes. In this approach, thepressure wave propagation in the hoses and pipes is neglected. The contact modeling isdivided into two stages: contact detection and contact response. Contact detectiondetermines when and where the contact occurs, and contact response provides the forceacting at the collision point. The friction between tire and ground is modelled using theLuGre friction model, which describes the frictional force between two surfaces.Typically, the equations of motion are solved in the full matrices format, where thesparsity of the matrices is not considered. Increasing the number of bodies and constraintequations leads to the system matrices becoming large and sparse in structure. To increasethe computational efficiency, a technique for solution of sparse matrices is proposed inthis dissertation and its implementation demonstrated. To assess the computingefficiency, augmented Lagrangian and semi-recursive methods are implementedemploying a sparse matrix technique. From the numerical example, the results show thatthe proposed approach is applicable and produced appropriate results within the real-timeperiod.